com.healthmarketscience.jackcess.util
Class CustomLinkResolver

java.lang.Object
  com.healthmarketscience.jackcess.util.CustomLinkResolver

All Implemented Interfaces:

LinkResolver

public abstract class CustomLinkResolver
extends Object
implements LinkResolver

Utility base implementaton of LinkResolver which facilitates loading linked tables from files which are not access databases. The LinkResolver API ultimately presents linked table information to the primary database using the jackcess Database and Table classes. In order to consume linked tables in non-mdb files, they need to somehow be coerced into the appropriate form. The approach taken by this utility is to make it easy to copy the external tables into a temporary mdb file for consumption by the primary database.

The primary features of this utility:

• Supports custom behavior for non-mdb files and default behavior for mdb files, see loadCustomFile(com.healthmarketscience.jackcess.Database, java.lang.String)
• Temp db can be an actual file or entirely in memory
• Linked tables are loaded on-demand, see loadCustomTable(com.healthmarketscience.jackcess.Database, java.lang.Object, java.lang.String)
• Temp db files will be automatically deleted on close

Author:

James Ahlborn

Field Summary

static Database.FileFormat	DEFAULT_FORMAT the default file format used for temp dbs
static boolean	DEFAULT_IN_MEMORY temp dbs default to the filesystem, not in memory
static File	DEFAULT_TEMP_DIR temp dbs end up in the system temp dir by default

Fields inherited from interface com.healthmarketscience.jackcess.util.LinkResolver

DEFAULT

Constructor Summary

protected	CustomLinkResolver() Creates a CustomLinkResolver using the default behavior for creating temp dbs, see DEFAULT_FORMAT, DEFAULT_IN_MEMORY and DEFAULT_TEMP_DIR.
protected	CustomLinkResolver(Database.FileFormat defaultFormat, boolean defaultInMemory, File defaultTempDir) Creates a CustomLinkResolver with the given default behavior for creating temp dbs.

Method Summary

protected Database	createTempDb(Object customFile, Database.FileFormat format, boolean inMemory, File tempDir) Creates a temporary database for holding the table data from linkeeFileName.
protected Database.FileFormat	getDefaultFormat()
protected File	getDefaultTempDirectory()
protected boolean	isDefaultInMemory()
protected abstract Object	loadCustomFile(Database linkerDb, String linkeeFileName) Called by resolveLinkedDatabase(com.healthmarketscience.jackcess.Database, java.lang.String) to determine whether the linkeeFileName should be treated as a custom file (thus utiliziing a temp db) or a normal access db (loaded via the default behavior).
protected abstract boolean	loadCustomTable(Database tempDb, Object customFile, String tableName) Called by an instance of a temp db when a missing table is first requested.
Database	resolveLinkedDatabase(Database linkerDb, String linkeeFileName) Custom implementation is:

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_FORMAT

public static final Database.FileFormat DEFAULT_FORMAT

the default file format used for temp dbs

DEFAULT_IN_MEMORY

public static final boolean DEFAULT_IN_MEMORY

temp dbs default to the filesystem, not in memory

See Also:

Constant Field Values

DEFAULT_TEMP_DIR

public static final File DEFAULT_TEMP_DIR

temp dbs end up in the system temp dir by default

Constructor Detail

CustomLinkResolver

protected CustomLinkResolver()

Creates a CustomLinkResolver using the default behavior for creating temp dbs, see DEFAULT_FORMAT, DEFAULT_IN_MEMORY and DEFAULT_TEMP_DIR.

CustomLinkResolver

protected CustomLinkResolver(Database.FileFormat defaultFormat,
                             boolean defaultInMemory,
                             File defaultTempDir)

Creates a CustomLinkResolver with the given default behavior for creating temp dbs.

Parameters:

defaultFormat - the default format for the temp db

defaultInMemory - whether or not the temp db should be entirely in memory by default (while this will be faster, it should only be used if table data is expected to fit entirely in memory)

defaultTempDir - the default temp dir for a file based temp db (null for the system defaqult temp directory)

Method Detail

getDefaultFormat

protected Database.FileFormat getDefaultFormat()

isDefaultInMemory

protected boolean isDefaultInMemory()

getDefaultTempDirectory

protected File getDefaultTempDirectory()

resolveLinkedDatabase

public Database resolveLinkedDatabase(Database linkerDb,
                                      String linkeeFileName)
                               throws IOException

Custom implementation is:

   // attempt to load the linkeeFileName as a custom file
   Object customFile = loadCustomFile(linkerDb, linkeeFileName);
   
   if(customFile != null) {
     // this is a custom file, create and return relevant temp db
     return createTempDb(customFile, getDefaultFormat(), isDefaultInMemory(),
                         getDefaultTempDirectory());
   }
   
   // not a custmom file, load using the default behavior
   return LinkResolver.DEFAULT.resolveLinkedDatabase(linkerDb, linkeeFileName);
 

Specified by:

resolveLinkedDatabase in interface LinkResolver

Throws:

IOException

See Also:

loadCustomFile(com.healthmarketscience.jackcess.Database, java.lang.String), createTempDb(java.lang.Object, com.healthmarketscience.jackcess.Database.FileFormat, boolean, java.io.File), LinkResolver.DEFAULT

createTempDb

protected Database createTempDb(Object customFile,
                                Database.FileFormat format,
                                boolean inMemory,
                                File tempDir)
                         throws IOException

Creates a temporary database for holding the table data from linkeeFileName.

Parameters:

customFile - custom file state returned from loadCustomFile(com.healthmarketscience.jackcess.Database, java.lang.String)

format - the access format for the temp db

inMemory - whether or not the temp db should be entirely in memory (while this will be faster, it should only be used if table data is expected to fit entirely in memory)

tempDir - the temp dir for a file based temp db (null for the system default temp directory)

Returns:

the temp db for holding the linked table info

Throws:

IOException

loadCustomFile

protected abstract Object loadCustomFile(Database linkerDb,
                                         String linkeeFileName)
                                  throws IOException

Called by resolveLinkedDatabase(com.healthmarketscience.jackcess.Database, java.lang.String) to determine whether the linkeeFileName should be treated as a custom file (thus utiliziing a temp db) or a normal access db (loaded via the default behavior). Loads any state necessary for subsequently loading data from linkeeFileName.

The returned custom file state object will be maintained with the temp db and passed to loadCustomTable(com.healthmarketscience.jackcess.Database, java.lang.Object, java.lang.String) whenever a new table needs to be loaded. Also, if this object is Closeable, it will be closed with the temp db.

Parameters:

linkerDb - the primary database in which the link is defined

linkeeFileName - the name of the linked file

Returns:

non-null if linkeeFileName should be treated as a custom file (using a temp db) or null if it should be treated as a normal access db.

Throws:

IOException

loadCustomTable

protected abstract boolean loadCustomTable(Database tempDb,
                                           Object customFile,
                                           String tableName)
                                    throws IOException

Called by an instance of a temp db when a missing table is first requested.

Parameters:

tempDb - the temp db instance which should be populated with the relevant table info for the given tableName

customFile - custom file state returned from loadCustomFile(com.healthmarketscience.jackcess.Database, java.lang.String)

tableName - the name of the table which is requested from the linked file

Returns:

true if the table was available in the linked file, false otherwise

Throws:

IOException